Differential pressure responsive damper

ABSTRACT

A damper comprising a plurality of parallel blades that are hinged on parallel axes and normally are opened in one direction by positive air pressure on a first side of the blades, for example, by the flow of air from an exhaust fan or the like. The damper blades are connected by linkage so that they swing together. The damper has a biased stop against which the blades close when the pressure differential between the two sides of the blades is negligible. When the pressure on the second side of the blade creates a predetermined positive pressure differential on the second side, the bias of the stop is overcome and the blades are opened in the opposite direction. The bias on the stop is variable in order to determine the pressure differential necessary to open the blades in the opposite direction.

[ July 30, 1.974

1 DIFFERENTIAL PRESSURE RESPONSIVE DAMPER [75] Inventor: Raymond L. Alley, Toledo, Ohio [73] Assignee: The American Warming &

REVERSE AIR Primary Examiner-Meyer Perlin Assistant Examiner-Ronald C. Capossela Attorney, Agent, or Firm-Henry K. Leonard [57] ABSTRACT A damper comprising a plurality of parallel blades that are hinged on parallel axes and normally are opened in one direction by positive air pressure on a first side of the blades, for example, by the flow of air from an exhaust fan or the like. The damper blades are connected by linkage so that they swing together. The damper has a biased stop against which the blades close when the pressure differential between the two sides of the blades is negligible. When the pressure on the second side of the blade creates a predetermined positive pressure differential on the second side, the bias of the stop is overcome and the blades are opened in the opposite direction. The bias on the stop is variable in order to determine the pressure differential necessary to open the blades in the opposite direction.

4 Claims, 4 Drawing Figures DIFFERENTIAL PRESSURE RESPONSIVE DAMPER BACKGROUND OF THE INVENTION Multiple blade dampers have long been utilized for preventing the backflow of air in exhaust ducts and for similar purposes, and frequently are installed in the outer walls of buildingsfrom which air is being exhausted, for example, by a power-driven fan or fans. Most of these dampers have a normal, closed position in which the multiple blades lie substantially in the same plane and are mounted on parallel pivots so that when a positive pressure differential exists between the inner side of the damper and the outer side of the damper, the air flow causes the damper blades to swing upwardly and outwardly, thereby providing for the escape of air being exhausted from the building. In conventional dampers of this type, however, in the event that a tornado passes the location of the building, the positive pressure differential on the outside of the building first forces the damper closed, but immediately, when the negative pressure phase of the tornado passes, the damper flies open allowing the positive pressure differential then in the building to reduce the negative pressure of the tornado. After the negative pressure phase of the tornado passes, the building interior frequently is below normal pressure and when normal pressure is restored outside the building, the damper is held closed so that the building implodes.

It has recently become a requirement in many buildings which are located in areas where tornados are experienced that means be provided by which the negative pressure inside the building under these conditions can rapidly be equalized to the restored normal or positive pressure outside the building so as to prevent such an implosion.

It is, therefore, a principal object of the instant invention to provide a damper which resists normal back drafts, but which is responsive to a predetermined pressure differential from the outer side of the damper toward the inner side allowing the damper to open in a reverse direction, thus to equalize the pressure between the inside and outside of the building in which the damper is located.

It is yet another object of the invention to provide a multi-blade damper which operates normally to allow the exhaust of air, which closes when there is a negligible pressure differential between the inside and the outside of the building, yet which is immediately responsive to the pressure differential resulting when the interior of the building is at a lower pressure than the outside of the building by a predetermined value and opens inwardly to obviate the damage resulting from an otherwise likely implosion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in elevation taken from the outer side of a damper embodying the invention;

FIG. 2 is a fragmentary view, partly in end elevation and partly in section taken along the line 2-2 of FIG.

. FIG. 3 is a fragmentary view, partly in section and partly in elevation, illustrating the normal operation of a damper embodying the invention to provide for the escape of air from the interior of a building; and

7 FIG. 4 is a fragmentary view, somewhat similar to FIG. 3, but shown on an enlarged scale and illustrating how a damper embodying the invention responds to the presence of reduced pressure inthe interior of the building and how the damper may be preset so that it thus responds upon the existence of a predetermined pressure differential.

DESCRIPTION OF PREFERRED EMBODIMENT A damper embodying the invention is generally indicated by the reference number 10 and may have a rectilinear frame fabricated from channels to provide side members 11 and 12 and top and bottom members 13 and 14, respectively. Several identical damper blades 15 are pivotally mounted by parallel horizontal axles 16 which extend across the damper l0 and are journalled by simple bearings 17 carried by the side members 11 and 12. Each of the blades 15 is shown as having what might be called an air foil shape, but the specific shape of the cross-section of the damper blades is not material to the invention.

Each of the axles 16 protrudes beyond a side member, in this case the side member 12, and a crank 18 is pinned or otherwise secured on the end of the axle 16, the free ends of the cranks 18 being pivotally connected to a vertically extending link bar 19 in order that all of the damper blades 15 will swing together in response to differential pressure between their opposite sides. Normally, i.e., when no differential pressure exists on opposite sides of the damper 10 and its blades 15, gravity causes the damper blades 15 to swing to their vertical aligned position wherein they all lie in substantially the same vertical plane and the damper is closed.

In this embodiment of the invention, the link bar 19 not only insures that all of the blades 15 swing together between their closed position (FIG. 2) and their normal open position (FIG. 3), but the bar 19 also cooperates with a stop, generally indicated by reference number 20, which is engaged by the bar 19 when the damper blades 15 are in their closed position in order to stop the blades in that position.

Under normal routine operations, a damper embodying the invention is intended to be installed, for example in the wall of a building or at the outer end of an exhaust duct, and to open outwardly (FIG. 3) in response to a flow of air through the duct created, for example, by a fan, or otherwise to open outwardly when there is a differential pressure between the inner and outer sides of the damper 10 and the pressure is higher on the inner side.

As mentioned above, however, a damper embodying the invention also is designed to provide protection against normally encountered back drafts and against unusual conditions in which the interior of the building or the duct upon which it is mounted has a pressure substantially lower than the exterior pressure, i.e., when the pressure differential is positive on the outer side of the damper or building.

The stop 20 in the illustrated embodiment of the invention comprises a horizontally slidable plunger 21 mounted in a sleeve 22 which, for example, is carried by a flange on a duct 23, or similar fixed structure, in the building or other location where the damper 10 is mounted. The plunger 21 is intended to slide back and forth in the sleeve 22, being biased forwardly by a coil spring 24 surrounding the plunger 21 and lying between one end of the sleeve 22 and an adjustable collar 25 mounted on the plunger 21. A stop collar 26 is adjustably positioned on the inner end of the plunger 21 behind the sleeve 22 in order to establish the normal position to which the spring 24 moves the plunger 21 and its contact roller 27 as shown in FIGS. 2 and 3. This normal position is maintained by the spring 24 and functions under normal conditions to stop the downward and inward movement of the link bar 19 when the damper l closes in the absence of a material pressure differential between its opposite sides.

By reason of the fact that the collar 25 is adjustable on the plunger 21, it is possible to predetermine the pressure differential at which a damper embodying the invention will function to relieve an abnormal pressure differential where the positive pressure is at the outer side of the damper allowing the damper blades to move to the position illustrated in FIG. 4. If desired, indicia generally indicated by the reference number 28 in FIG. 4 may be provided on the plunger 21 to enable the position of the collar 25 to be set without empirical test. For example, a damper embodying the invention readily may be designed which will open in either direction under a differential pressure build up at a rate of l psig per second. In other words, unless there exists a pressure differential between the outer and inner sides 7 of the damper wherein the build up is greater than 1 psig, the damper blades 15 will remain in their normal closed position, being held therein by the bias of the spring 24 as determined by the position of the sliding adjustable collar 25.

Under tornado conditions, however, if the interior of the enclosure in which the damper 10 is located should drop to less than normal then, upon restoration of normal or greater than normal pressure exteriorally of the building, the pressure differential acting on the damper blades in this opposite direction would overcome the bias of the spring 24. The pressure acting on the blades 15 would then swing them inwardly to the position illustrated in FIG. 4 with the link bar 19 acting against the roller 27 to thrust the plunger 21 inwardly, compressing the spring 24 to the degree necessary to equalize the pressure between the exterior and interior of the building, thus effectively obviating the likelihood of an implosion of the building occurring at this point.

Under normal atmospheric conditions, however, as pointed out above, the damper embodying the invention functions to prevent back drafts into the building or duct such as might occur in a normal storm with immaterial increases in exterior pressure or build-up of exterior pressure at a rate less, for example, than I psig per second.

What I claim is:

l. A damper having a plurality of rectangular blades that are hingedly mounted on parallel axes extending along corresponding edges of said blades, the axes being spaced from each other a distance substantially equal to the width of the blades normal to said axes, means linking said blades for pivotal movement together, said blades being freely movable in one direction from closed, aligned position to open parallel position by a positive pressure differential on one side of said blades, biased stop means for normally preventing movement of said blades from closed position to open position in the opposite direction, and means for varying the bias on said stop means, whereby a predetermined positive pressure differential on the opposite side of said blades overcomes the bias on said stop means and causes said blades to move in the opposite direction from closed position to open position.

2. A damper according to claim '1 in which the stop means is biased by a spring.

3. A damper according to claim 1 in which the stop means consists of a plunger biased by a coil spring engaged between a fixed plunger guide and a collar on said plunger.

4. A damper according to claim 1 in which the rectangular blades extend horizontally, are pivoted along their upper edges and lie in a vertical plane when closed. 

1. A damper having a plurality of rectangular blades that are hingedly mounted on parallel axes extending along corresponding edges of said blades, the axes being spaced from each other a distance substantially equal to the width of the blades normal to said axes, means linking said blades for pivotal movement together, said blades being freely movable in one direction from closed, aligned position to open parallel position by a positive pressure differential on one side of said blades, biased stop means for normally preventing movement of said blades from closed position to open position in the opposite direction, and means for varying the bias on said stop means, whereby a predetermined positive pressure differential on the opposite side of said blades overcomes the bias on said stop means and causes said blades to move in the opposite direction from closed position to open position.
 2. A damper according to claim 1 in which the stop means is biased by a spring.
 3. A damper according to claim 1 in which the stop means consists of a plunger biased by a coil spring engaged between a fixed plunger guide and a collar on said plunger.
 4. A damper according to claim 1 in which the rectangular blades extend horizontally, are pivoted along their upper edges and lie in a vertical plane when closed. 